Core-shell morphology of composite filaments for use in extrusion-based additive manufacturing systems

ABSTRACT

A consumable filament for use in an extrusion-based additive manufacturing system, where the consumable filament comprises a core portion of a matrix of a first base polymer and particles dispersed within the matrix, and a shell portion comprising a same or a different base polymer. The consumable filament is configured to be melted and extruded to form roads of a plurality of solidified layers of a three-dimensional part, and where the roads at least partially retain cross-sectional profiles corresponding to the core portion and the shell portion of the consumable filament and retain the particles within the roads of the printed part and do not penetrate the outer surface of the shell portion.

BACKGROUND

The present disclosure relates to additive manufacturing systems forprinting three-dimensional (3D) parts and support structures. Inparticular, the present disclosure relates to materials for use inadditive manufacturing systems, consumable assemblies retaining thematerials, and methods of manufacturing and using the materials andassemblies in additive manufacturing systems to print 3D parts. Allreferences disclosed herein are incorporated by reference.

Additive manufacturing systems are used to build 3D parts from digitalrepresentations of the 3D parts (e.g., STL format files) using one ormore additive manufacturing techniques. Examples of commerciallyavailable additive manufacturing techniques include extrusion-basedtechniques, ink jetting, selective laser sintering, powder/binderjetting, electron-beam melting, and stereolithographic processes. Foreach of these techniques, the digital representation of the 3D part isinitially sliced into multiple horizontal layers. For each sliced layer,a tool path is then generated, which provides instructions for theparticular additive manufacturing system to form the given layer.

For example, in an extrusion-based additive manufacturing system, a 3Dpart or model may be printed from a digital representation of the 3Dpart in a layer-by-layer manner by extruding a flowable part material.The part material is extruded through an extrusion tip carried by aprint head of the system, and is deposited as a sequence of roads on asubstrate in an x-y plane. The extruded part material fuses topreviously deposited part material, and solidifies upon a drop intemperature. The position of the print head relative to the substrate isthen incremented along a z-axis (perpendicular to the x-y plane), andthe process is then repeated to form a 3D part resembling the digitalrepresentation.

In fabricating 3D parts by depositing layers of a part material,supporting layers or structures are typically built underneathoverhanging portions or in cavities of objects under construction, whichare not supported by the part material itself. A support structure maybe built utilizing the same deposition techniques by which the partmaterial is deposited. The host computer generates additional geometryacting as a support structure for the overhanging or free-space segmentsof the 3D part being formed. Support material is then deposited from asecond nozzle pursuant to the generated geometry during the printingprocess. The support material adheres to the modeling material duringfabrication, and is removable from the completed 3D part when theprinting process is complete.

SUMMARY

In a first aspect, the present disclosure is directed to a consumablefilament for use in an extrusion-based additive manufacturing system.The consumable filament includes a core portion extending along alongitudinal length of the consumable filament, the core portioncompositionally comprising a matrix of a first base polymer andparticles dispersed within the matrix and a shell portion extendingalong the longitudinal length of the consumable filament and at leastpartially encasing the core portion, the shell portion compositionallycomprising a second base polymer, wherein the consumable filament isconfigured to be melted and extruded in an additive manufacturingsystem. The first base polymer and the second base polymer may be thesame. The first base polymer and the second base polymer may bedifferent. The particles in the core portion may be selected frommetallic particles, non-metallic particles, magnetic particles andcombinations thereof. The particles may be ferrite particles. Theparticles may be at least about 50 percent by volume of the core portionvolume. The consumable filament may have a geometry selected from acylinder, a ribbon, a tube and other filled or hollow profiles. Theshell portion may be acrylonitrile styrene acrylate (ASA) and the coreportion may be a matrix of ASA and ferrite particles.

In another aspect, the present disclosure is directed to a printed partbuilt with an extrusion-based additive manufacturing system. The printedpart includes a plurality of solidified layers each comprising roadsextruded with the extrusion-based additive manufacturing system from aconsumable filament having a core portion and a shell portion, whereinthe core portion compositionally comprises a matrix of a first basepolymer and particles dispersed within the matrix, and wherein the shellportion comprises a second base polymer; and wherein the plurality ofsolidified layers retain the particles substantially within the coreportion of the consumable filament and at least partially retain thecross-sectional profiles corresponding to the core portion and the shellportion of the consumable filament. The first base polymer and thesecond base polymer may be the same. The first base polymer and thesecond base polymer may be different. The particles in the core portionmay be selected from metallic particles, non-metallic particles,magnetic particles and combinations thereof. The particles may beferrite particles. The particles may be at least about 50 percent byvolume of the core portion volume. The shell portion may be ASA and thecore portion may be a matrix of ASA and ferrite particles.

In a further aspect, the present disclosure is directed to a method forbuilding a three-dimensional part with an additive manufacturing systemhaving an extrusion head. The method includes providing a consumablefilament to the extrusion head, the consumable filament comprising acore portion and a shell portion substantially encasing the coreportion, wherein the core portion compositionally comprises a matrix ofa first base polymer and particles dispersed within the matrix, andwherein the second portion compositionally comprises a second basepolymer. The printing step may include melting the fed consumablefilament in the extrusion head to form a molten material, depositing themolten material in a build environment as extruded roads that defines alayer of the three-dimensional object and solidifying the extrudedroads, wherein the solidified roads at least partially retaincross-sectional profiles corresponding to the core portion and the shellportion of the consumable filament and retain the particles within theextruded roads. The first base polymer and the second base polymer maybe the same. The first base polymer and the second base polymer may bedifferent. The particles in the core portion may be selected frommetallic particles, non-metallic particles, magnetic particles andcombinations thereof. The particles may be ferrite particles. Theparticles may be at least about 50 percent by volume of the core portionvolume. The shell portion may be Acrylonitrile Styrene Acrylate (ASA)and the core portion may be ASA-ferrite.

In yet a further aspect, the present disclosure is directed to a methodof making a consumable filament for use in an additive manufacturingsystem. The method includes extruding a consumable filament for use inan additive manufacturing system, the consumable filament comprising acore portion and a shell portion that substantially encases the coreportion, wherein the core portion and the shell portion are coextruded,the core portion compositionally comprising a matrix of a first basepolymer and particles dispersed within the matrix and the second portioncompositionally comprising a second base polymer. The extrusion of thecore portion may use a lead screw extruder. The extrusion of the shellportion may use a pressure limited extruder. The ratio of the coreportion volume to the shell portion volume can be varied by increasingthe speed of core portion extrusion. The core portion can be betweenabout 50 percent by volume and about 95 percent by volume of theconsumable filament. The particles may be selected from metallicparticles, non-metallic particles, magnetic particles and combinationsthereof.

DEFINITIONS

Unless otherwise specified, the following terms used in thisspecification have the meanings provided below.

The term “polymer” refers to a polymeric material having one or moremonomer species, including homopolymers, copolymers, terpolymers, andthe like.

Reference to “a” chemical compound refers one or more molecules of thechemical compound, rather than being limited to a single molecule of thechemical compound. Furthermore, the one or more molecules may or may notbe identical, so long as they fall under the category of the chemicalcompound. Thus, for example, “a” polyamide is interpreted to include oneor more polymer molecules of the polyamide, where the polymer moleculesmay or may not be identical (e.g., different molecular weights and/orisomers).

The terms “at least one” and “one or more of” an element are usedinterchangeably, and have the same meaning that includes a singleelement and a plurality of the elements, and may also be represented bythe suffix “(s)” at the end of the element. For example, “at least onepolyamide”, “one or more polyamides”, and “polyamide(s)” may be usedinterchangeably and have the same meaning.

The term “three-dimensional part” refers to any part built using alayer-based additive manufacturing technique, and includes 3D parts andsupport structures built using layer-based additive manufacturingtechniques.

Directional orientations such as “above”, “below”, “top”, “bottom”, andthe like are made with reference to a layer-printing direction of a 3Dpart. In the embodiments shown below, the layer-printing direction isthe upward direction along the vertical z-axis. In these embodiments,the terms “above”, “below”, “top”, “bottom”, and the like are based onthe vertical z-axis. However, in embodiments in which the layers of 3Dparts are printed along a different axis, such as along a horizontalx-axis or y-axis, the terms “above”, “below”, “top”, “bottom”, and thelike are relative to the given axis.

Unless otherwise specified, characteristics of a material or a 3D partprinted from the material refer to the characteristics as measuredparallel to the orientation of the 3D part layers and perpendicular tothe layer-printing direction, and is referred to as a “xy-direction”.Correspondingly, the term “z-direction”, with reference tocharacteristics of a material or a 3D part printed from the materialrefer to the characteristics as measured perpendicular to theorientation of the 3D part layers and parallel to the layer-printingdirection. Unless the measurement direction is specified as “in thez-direction”, a measurement referred to herein is taken in thexy-direction. For example, a tensile strength of a 3D part of 10,000 psirefers to a tensile strength measured parallel to the layers of the 3Dpart. Alternatively, a tensile strength of a 3D part in the z-directionof 8,000 psi refers to a tensile strength measured perpendicular to thelayers of the 3D part.

Unless otherwise specified, temperatures referred to herein are based onatmospheric pressure (i.e. one atmosphere).

The term “additive manufacturing system” refers to a system that prints,builds, or otherwise produces 3D parts and/or support structures atleast in part using an additive manufacturing technique. The additivemanufacturing system may be a stand-alone unit, a sub-unit of a largersystem or production line, and/or may include other non-additivemanufacturing features, such as subtractive-manufacturing features,pick-and-place features, two-dimensional printing features, and thelike.

The term “providing”, such as for “providing a consumable material”,when recited in the claims, is not intended to require any particulardelivery or receipt of the provided part. Rather, the term “providing”is merely used to recite parts that will be referred to in subsequentelements of the claim(s), for purposes of clarity and ease ofreadability.

The terms “preferred”, “preferably”, “example” and “exemplary” refer toembodiments of the invention that may afford certain benefits, undercertain circumstances. However, other embodiments may also be preferredor exemplary, under the same or other circumstances. Furthermore, therecitation of one or more preferred or exemplary embodiments does notimply that other embodiments are not useful, and is not intended toexclude other embodiments from the scope of the present disclosure.

The terms “about” and “substantially” are used herein with respect tomeasurable values and ranges due to expected variations known to thoseskilled in the art (e.g., limitations and variabilities inmeasurements).

The terms “core portion” and “shell portion” of a filament refer torelative locations of the portions along a cross-section of the filamentthat is orthogonal to a longitudinal length of the filament, where thecore portion is an inner portion relative to the shell portion. Unlessotherwise stated, these terms are not intended to imply any furtherlimitations on the cross-sectional characteristics of the portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an extrusion-based additive manufacturingsystem for building printed parts with the use of consumable materialsof the present disclosure.

FIG. 2 is a perspective view of a segment of a consumable filament ofthe present disclosure, where the consumable filament includes a coreportion and a shell portion.

FIG. 3 is a perspective view of a segment of an exemplary consumablefilament of the present disclosure, where the exemplary consumablefilament includes a rectangular cross-sectional geometry.

FIG. 4 is a plan view of an exemplary co-extrusion process formanufacturing a consumable filament including a core portion and a shellportion.

FIG. 5 is a series of photographs of cross-sections of filaments showingthe variation of the shell portion with the increase in extrusion speedof the core portion.

FIG. 6 is a side illustration of layers of a printed part during a buildoperation, where the dimensions of the layers and the relative distanceof an extrusion tip from the layers are exaggerated for ease ofdiscussion.

FIG. 7 is a series of photographs of a cross-section of a printed partusing a filament with a core portion and a shell portion of the presentdisclosure with variation of a thickness of the shell portion.

DETAILED DESCRIPTION

The present disclosure is directed to consumable materials, e.g.consumable composite filaments, for use in extrusion-based additivemanufacturing systems, where the consumable materials have core-shellconfigurations. The core-shell configurations include a core portion anda shell portion where the core portion and the shell portioncompositionally include base polymers. The base polymers of the coreportion and the shell portion may be the same or different. The coreportion can further include particles dispersed within the polymericmatrix of the core portion. These particles can be metallic particlessuch as ferrite particles. Composite filaments having these compositionsimpart different properties that can be used to produce printed parts,such as ferromagnetic parts. As discussed below, the differentproperties of these materials may assist with the build operations inthe extrusion-based additive manufacturing systems and may also increasethe capability to print parts with different physical properties.

Consumable materials of the present description include a core portionthat can compositionally include a matrix of a first base polymer and ashell portion that can compositionally include a same or a differentbase polymer. The core portion can further include particles, such asmetallic particles, dispersed in the polymeric matrix. As discussedfurther below, consumable filaments where the particles are retainedwithin the core portion desirably have fewer filament breaks duringprinting, reduced degradation of the extrusion nozzle performance in theadditive manufacturing systems and other wear issues on the machineryrelated to the presence of particles in the consumable materials withoutthe shell layer. The resulting printed parts may accordingly be builtwith good dimensional accuracies and with good interlayer z-bondstrengths while imparting mechanical properties that otherwise could notbe previously printed due to the brittle properties of the core matrix.

Extrusion-based additive manufacturing systems currently build printedparts with consumable materials that include a variety of thermoplasticpolymeric materials. The thermoplastic polymeric materials can beamorphous or semi-crystalline polymeric materials, such as, but notlimited to, acrylonitrile-butadiene-styrene (ABS) resins, ASA resins andpolycarbonate resins. Amorphous polymeric materials have little or noordered arrangements of their polymer chains in their solid states. Assuch, these materials exhibit glass transition effects that render themsuitable for building printed parts and support structures inextrusion-based additive manufacturing systems. For example, asdisclosed in Batchelder, U.S. Pat. No. 5,866,058, an amorphous polymericmaterial may be deposited into a build region maintained at atemperature that is between a solidification temperature and a glasstransition temperature of the material. This reduces the effects ofcurling and plastic deformation in the resulting printed part or supportstructure. Semi-crystalline materials or materials having both amorphousand semi-crystalline materials can also be used.

As shown in FIG. 1, system 10 is an extrusion-based additivemanufacturing system for building printed part with a composite filamentdisclosed herein. As such, the resulting printed parts may be built withthe polymeric materials and particles, while exhibiting reducedbrittleness characteristic of composite filaments being fed to theextrusion head due to the shell substantially encasing the core.Examples of suitable systems for system 10 include extrusion-basedadditive manufacturing systems, such as those commercially availablefrom Stratasys, Inc., Eden Prairie, Minn. under the trade designation“FDM”.

System 10 includes build chamber 12, build substrate 14, gantry 16,extrusion head 18, and supply sources 20 and 22. Build chamber 12 is anenclosed, heatable environment that contains build substrate 14, gantry16, and extrusion head 18 for building a printed part (referred to asprinted part 24) and a corresponding support structure (referred to assupport structure 26). However, other build environments are alsocontemplated, such as, but not limited to non-heated build chambers orout of oven build environments. Build substrate 14 can be a platform onwhich printed part 24 and support structure 26 are built, and desirablymoves along a vertical z-axis based on signals provided fromcomputer-operated controller 28. Build substrate 14 may also include apolymeric film (not shown) to further facilitate the removal of printedpart 24 and support structure 26. Alternatively, printed part 24 andsupport structure 26 may be built on a build tray. The build tray mayinclude a polymeric film to facilitate the removal of the printed partand the support structure.

Gantry 16 is a guide rail system that is desirably configured to moveextrusion head 18 in a horizontal x-y plane within build chamber 12based on signals provided from controller 28. The horizontal x-y planeis a plane defined by an x-axis and a y-axis (not shown), where thex-axis, the y-axis, and the z-axis are orthogonal to each other. In analternative embodiment, build substrate 14 may be configured to move inthe horizontal x-y plane within build chamber 12, and extrusion head 18may be configured to move along the z-axis. Other similar arrangementsmay also be used such that one or both of build substrate 14 andextrusion head 18 are moveable relative to each other.

Extrusion head 18 is supported by gantry 16 for building printed part 24and support structure 26 on build substrate 14 in a layer-by-layermanner, based on signals provided from controller 28. In the embodimentshown in FIG. 1, extrusion head 18 is a dual-tip extrusion headconfigured to deposit materials from supply source 20 and supply source22, respectively. Examples of suitable extrusion heads for extrusionhead 18 include those disclosed in Crump et al., U.S. Pat. No.5,503,785; Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al.,U.S. Pat. No. 7,604,470; and Leavitt, U.S. Pat. No. 7,625,200.Furthermore, system 10 may include a plurality of extrusion heads 18 fordepositing modeling and/or support materials.

The composite filaments of the present disclosure may be used as themodeling material for building printed part 24. As such, the compositefilament may be supplied to extrusion head 18 from supply source 20 viafeed line 30, thereby allowing extrusion head 18 to melt and deposit thecomposite polymeric materials as a series of extruded roads to buildprinted part 24 in a layer-by-layer manner. Correspondingly, the supportmaterial may be supplied to extrusion head 18 from supply source 22 viafeed line 32, thereby allowing extrusion head 18 to melt and deposit thesupport material as a series of extruded roads to build supportstructure 26 in a layer-by-layer manner. Suitable devices for supplysources 20 and 22 include those disclosed in Swanson et al., U.S. Pat.No. 6,923,634; Comb et al., U.S. Pat. No. 7,122,246; and Taatjes et al,U.S. Pat. Nos. 7,938,351 and 7,938,356. In one embodiment, the supportmaterial used to build support structure 26 may be an amorphouspolymeric material, such as the water-soluble and break-away supportmaterials commercially available from Stratasys, Inc., Eden Prairie,Minn.

During a build operation, gantry 16 moves extrusion head 18 around inthe horizontal x-y plane within build chamber 12, and one or more drivemechanisms are directed to intermittently feed the modeling and supportmaterials through extrusion head 18 from supply sources 20 and 22.Examples of suitable drive mechanisms for use in extrusion head 18include those disclosed in Crump et al., U.S. Pat. No. 5,503,785;Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al., U.S. Pat.Nos. 7,384,255 and 7,604,470; Leavitt, U.S. Pat. No. 7,625,200; andBatchelder et al., U.S. Pat. No. 7,896,209.

The received modeling and support materials are then deposited ontobuild substrate 14 to build printed part 24 and support structure 26 asextruded roads using a layer-based additive manufacturing technique.Support structure 26 is desirably deposited to provide vertical supportalong the z-axis for overhanging regions of the layers of printed part24. This allows 3D part 24 to be built with a variety of geometries.After the build operation is complete, the resulting printed part24/support structure 26 may be removed from build chamber 12. Supportstructure 26 may then be removed from printed part 24. For example, inembodiments in which the support material is water soluble, theresulting printed part 24/support structure 26 may be placed in a bathcontaining an aqueous liquid and/or solution (e.g., an aqueous alkalinesolution) to remove support structure 26 from printed part 24.

FIG. 2 illustrates a segment of filament 34, which is an example of asuitable consumable, composite filament of the present disclosure. Asshown, filament 34 includes core portion 36 and shell portion 38, whichextend along longitudinal length 40. Core portion 36 is the innerportion of filament 34, located along central axis 42, and shell portion38 is the outer portion of filament 34, and defines to outer surface 44.Core portion 36 compositionally includes a matrix of a base polymer,particles 50 and optionally, one or more additives. Shell portion 38compositionally includes a base polymer and optionally, one or moreadditives. The base polymer of the shell material may be the same as thebase polymer of the core material. In some embodiments, the base polymerof the core material may be different than the base polymer of the shellmaterial. Preferably, the core materials and the shell materials arecompatible for substantially retaining the particles within the coreportion.

The core and shell materials can each include one or more thermoplasticpolymers, and optionally, one or more additives. The thermoplasticpolymers can be amorphous polymers or semi-crystalline polymers. Thecore and shell materials, for example, may include additives to modify,for example, the rheology, the glass transition temperature, and thelike. Examples of suitable thermoplastic base polymers for use in eachof the core and/or shell materials can includeacrylonitrile-butadiene-styrene (ABS) copolymers, acrylonitrile styreneacrylate (ASA), styrene-acrylonitrile resin (SAN), polylactic acid(PLA), cyclic olefin copolymer (COC), polyethylene terephthalate(PET-G), polyetheretherketone (PEEK) or polyetherketoneketone (PEKK)family, polycarbonates, polysulfones, polyethersulfones,polyphenylsulfones, polyetherimides, polyamides modified variationsthereof (e.g., Nylon-12 copolymers manufactured by Stratasys, Inc.located in Eden Prairie, Minn.), polystyrene, polypropylenes,copolyesters, and blends thereof. Unless indicated otherwise, the basepolymers for the core and shell materials are not intended to be limitedto these listed polymers.

In another embodiment, the core and shell materials may includethermoplastic polymers derived from the same or similar monomer units,but have different molecular properties, such as different relativemolar masses, different molecular weights, different terminal groupchemistries, different stereochemistries, and combinations thereof.

In an exemplary embodiment, the core and/or shell materials of theconsumable filament include acrylonitrile styrene acrylate (ASA). Thecore and/or shell materials can include ASA alone or combined with otherbase polymers. A source ASA filament material is Stratasys, Inc. locatedin Eden Prairie, Minn. However, the present disclosure is not limited toASA.

The core portion of the composite filaments described herein can furtherinclude particles. Suitable particles can be particles derived from avariety of materials. Inclusion of the particles in the core portion ofconsumable materials having a core/shell morphology is advantageous dueto the protective shell portion (without the particles) substantiallyencasing the core portion with the particles. The protective shellportion can improve the durability of the filaments, reduce thebrittleness of a filament having only the core components and/or reducethe degradation of drives, liquifiers, tubes, liquefier tips and otherparts within extrusion head 18 that would contact the particles in acomposite filament. The core/shell morphology of the composite filamentcan be protective against the wear of parts due to the fact theparticles are substantially or completely retained in the core portionof the filament and/or without penetrating the outer surface of theshell portion. Therefore, substantially all or all of the particles donot contact the parts of the extruder.

In some embodiments, particles that can be included in the core portioninclude metallic particles. Metallic particles may be magnetic particlesand/or non-magnetic particles. Particles can include metallic,non-magnetic particles, for example, aluminum, copper, gold, silver,stainless steel, titanium, combinations thereof and the like. Particlescan also include metallic magnetic particles, for example, iron, cobaltand nickel combinations thereof and the like. Non-metallic particles canalso be included in the core material and are also within the scope ofthis disclosure. Examples of non-metallic particles include particleswith thermoplastic polymers having different properties such as meltingtemperature from the base polymers of the core and the shell.Non-metallic particles can include ceramic particles. Particles can alsoinclude moisture absorbing particles, thermally conductive particles,glass bead particles and combinations thereof to aid in processing. Theparticles may also be organic fill, e.g. cellulose, rice hulls and thelike. The particles may have a regular shape such as spheres or cubes orthey may have an irregular shape. The core portion of a compositefilament may include only one type of particles. Alternatively, the coreportion of a composite filament may include two or more types ofparticles, e.g. ferrite and stainless steel particles. The selection ofthe particles or filler can be dependent on the application, e.g.tungsten and barium sulfide for radiopaque applications.

In one exemplary embodiment, the particles included in the compositefilament are preferably ferrite particles. The ferrite particles, forexample, can be combined with the base polymer of the core material. Anexemplary filament can include, for example, a core material of a matrixof ASA with ferrite particles as the core. Furthermore, the shellmaterial can also include ASA as the shell. Shell material and corematerial other than ASA may also be suitable and is within the scope ofthis disclosure.

The number of particles that can be included in the filament of theconsumable material can vary and can be dependent on the end use of thefilament and the desired printed part. Particles can be in the core butsome particles may also be in the shell. The particles in the filamentcan be at least about 20 percent by volume of the core portion.Preferably, the particles in the filament are at least about 50 percentby volume of the core portion and more preferably, at least about 55percent by volume of the core portion. It is contemplated that an upperlimit of the volume percent of the particles in the core portion isdictated by the ability to extrude the particles in a matrix thatretains as the configuration of the extrudate. Otherwise stated, theupper limit of the volume percent of the particles is limited by theability of the polymer to retain the particles in the configuration ofthe extrudate and the interfacial modification chemistries used to coatthe particles. The upper limit of the particles may be, for example,about 85 percent by volume of the core portion. Percentage of particlesgreater than about 85 percent by volume of the core portion are alsowithin the scope of this disclosure.

The size of the particles can vary and can be dependent on the specificparticles used, the thickness of the core portion and the shell portion,the desired end use of the filament and the like. Particle size can belimited by the extrusion nozzle inner diameter ID and angle such thatparticles could not stack or bridge. In some embodiments, the upperlimit to particle size may be about one third of the inner extrusionnozzle diameter. In one exemplary embodiment, the size of the particlescan be between about 10 microns and about 200 microns.

The core materials and shell materials of a composite filament areselected based on the desired characteristics or properties of theprinted part. Utilizing the present core shell filament allows thedesired properties to be provided by the core portion while the shellportion aids in transporting the core portion to the extrusion head.

Core portion 36 and shell portion 38, as illustrated in FIG. 2 has adefined interface. In the filaments of the present disclosure, theviscosity of the core portion and the viscosity of the shell portion canbe mismatched due to the presence of the particles. This mismatch of theviscosity can occur even when the base polymer of the core portion andthe base polymer of the shell portion are the same or substantiallysimilar. Without being bound by any theory, the viscosity between thecore portion and the shell portion can be different while maintaininglaminar flow of the core/shell materials in the liquefier of anextrusion based additive manufacturing system such as system 10 shown inFIG. 1. While core portion 36 and shell portion 38 are illustrated inFIG. 2 as having a defined interface, it is understood that the core andshell materials may partially interdiffuse at this interface during theextrusion process, particularly when the viscosities are the same. Coreportions and shell portions having the same or similar viscosities arealso within the scope of this disclosure.

Furthermore, the melting temperatures of the core materials (excludingthe particles) and shell materials are desirably the same or similar toallow filament 34 to be readily melted in a liquefier of extrusion head18. As such, the base polymers and optionally any additives of the corematerial (excluding the particles) and the shell material may beselected to minimize the differences in melting temperatures.

Core portions and shell portions with different melting temperatures arealso within the scope of the disclosure. In these embodiments, meltingtemperatures of the core portion and shell portion are amenable toretaining the particles within the core portion and/or withoutpenetrating the exterior surface of the shell portion when melted in aliquefier of extrusion head 18 of an additive manufacturing system.

In alternative embodiments, the core materials and shell materials mayinclude the same or similar base polymers, but the core material caninclude one or more additives that can change its characteristics, e.g.rheology, glass transition temperature, T_(g), melting temperature andthe like. Furthermore, the shell material may also include one or moreadditives to alter its characteristics.

In other alternative embodiments, the core materials and the shellmaterials can be different. They can, for example, include differentbase polymers and different additives. In these embodiments, even thoughthe base polymers and/or the additives may be different, the corematerial and the shell material may still be compatible if the coreportion and shell portion can exhibit similar characteristics orproperties, e.g. rheological properties, T_(g) and/or the meltingtemperature, as described above. For example, the T_(g) temperature of abase polymer in the core materials can be changed to match or becompatible with the T_(g) temperature of the shell materials byincluding additives to the core materials that can change the T_(g)temperature. Thus, even though the base polymers are different, thematerials can be compatible for the core portion and the shell portionof the consumable filaments. Accordingly, the core and shell materialsmay include a variety of compositional combinations to attain a desiredsimilarity in rheology, T_(g) temperatures and the like. Incompatiblematerials could be used together by using a tie-layer of polymer betweenthe core and the shell. A tie layer is a material that is compatiblewith both of the other polymers that may not be compatible with oneanother.

Core/shell materials with different characteristics can also be withinthe scope of the present disclosure as long as the particles areretained within the interior portion of the filament during extrusion ofthe filament. In addition, core/shell materials are selected such thatthe particles do not penetrate the outer surface of the shell portion asthe filament is melted within the liquefier tube. Furthermore, theparticles do not penetrate the outer surface of the shell portion duringextrusion and printing a part in a layer by layer manner with anadditive manufacturing system.

In addition to the base polymer(s), the core portion and/or the shellportion of the present disclosure may also include additional additives,such as impact modifiers, plasticizers, rheology modifiers, inertfillers, colorants, stabilizers, and combinations thereof. Inembodiments that include colorants, preferred concentrations of thecolorants in the core and/or the shell materials range from about 0.1%to about 5% by weight. Suitable colorants include titanium dioxide,barium sulfate, carbon black, and iron oxide, and may also includeorganic dyes and pigments.

In embodiments that include fillers, preferred concentrations of thefillers in the core materials and/or shell materials range from about 1%to about 80% by weight. Suitable fillers include calcium carbonate,magnesium carbonate, glass spheres, graphite, carbon black, carbonfiber, glass fiber, talc, wollastonite, mica, alumina, silica, kaolin,silicon carbide, zirconium tungstate, soluble salts, and combinationsthereof.

In embodiments that include plasticizers, preferred concentrations ofthe plasticizers in the core materials and/or the shell materials rangefrom about 0.5% to about 20% by weight. Suitable additional plasticizersfor use in the core materials and/or shell materials include dialkylphthalates, cycloalkyl phthalates, benzyl and aryl phthalates, alkoxyphthalates, alkyl/aryl phosphates, polyglycol esters, adipate esters,citrate esters, esters of glycerin, and combinations thereof.

In the shown embodiment (FIG. 2), filament 34 has a cylindricalgeometry. Core portion 36 has an outer diameter referred to as corediameter 36 d, and shell portion 38 has an outer diameter referred to asshell diameter 38 d, where shell diameter 38 d also corresponds to theouter diameter of filament 34. The relative dimensions for shelldiameter 38 d to core diameter 36 d are desirably selected such that theamount of the shell material that is extruded falls within a balancedrange for use in system 10 (shown in FIG. 1).

Filament 34 can have alternative geometries in addition to cylindricalgeometries and all are within the scope of this disclosure. Othernon-cylindrical geometries include, for example, a ribbon, a tube andother solid and hollow profiles. The cross-sectional geometry of thefilament can include, for example, oval, oblong, round, rectangular,triangular, star-shaped, and the like. Filament 34 can be a ribbonfilament and have a square or rectangular geometry as shown, forexample, in FIG. 3. The filaments may have solid or hollow profiles. Thefilament, for example, can include a tube or other solid or hollowprofiles. The filament can also be, for example, a tube or a cylinderwith three or more layers wherein the outer and the inner layers mayhave same or different materials and include a layer with particlessandwiched between the inner and outer layers. In one exemplaryembodiment, the filament includes an A-B-A layer configuration whereinthe inner and outer layer include the same material (A) and the middlelayer (B) with the material and particles is sandwiched between the two(A) layers. Filaments with other multilayer arrangements and shapes arealso within the scope of this disclosure.

The amount of the shell material in filament 34 is desirably high enoughsuch that the extruded roads used to build each layer of printed part 24(shown in FIG. 1) have sufficient quantities of the shell material(which solidifies upon deposition and cooling in build chamber 12) tokeep the particles within the core material and/or encased within theshell material and to resist the pressures exerted on the extruded roadsduring the formation of subsequent layers of printed part 24. On theother end, the amount of the shell material is desirably low enough toprevent substantial distortions of printed part 24 upon deposition.While not wishing to be bound to theory, it is believed that thedifference in density of the core and the shell, the denser core havingthe particulate has a tendency to sink into and deform the thickersubstantially polymeric shell, which can result in distortions of theextruded roads and the printed part.

The amount of the shell material in filament 34 may be determined bydividing the average volume of shell portion 38 from the overall averagevolume of filament 34 (i.e., the sum of the average volumes of coreportion 36 and shell portion 38). The average diameters, cross-sectionalareas, and volumes referred to herein are based on average measurementstaken for a suitable segment of filament 34 along longitudinal length40, such as a distance of 6.1 meters (20 feet).

In embodiments in which core diameter 36 d and shell diameter 38 d areeach substantially uniform along longitudinal length 40, measurements ofthe volumes of shell portion 38 and filament 34 may be simplified tofunctions of the respective cross-sectional areas. For cylindricalfilament 34, the cross-sectional areas for core portion 36, shellportion 38, and filament 34 may be determined based on core diameter 36d and shell diameter 38 d.

Examples of suitable average diameters for core diameter 36 d range fromabout 0.76 millimeters (about 0.03 inches) to about 2.5 millimeters(about 0.10 inches). In one embodiment, suitable average diameters forcore diameter 36 d range from about 1.0 millimeter (about 0.04 inches)to about 1.5 millimeters (about 0.06 inches). Examples of suitableaverage diameters for shell diameter 38 d range from about 1.0millimeter (about 0.04 inches) to about 3.0 millimeters (about 0.12inches). In one embodiment, suitable average diameters for shelldiameter 38 d range from about 1.0 millimeter (about 0.04 inches) toabout 1.5 millimeters (about 0.06 inches). In another embodiment,suitable average diameters for shell diameter 38 d range from about 1.5millimeters (about 0.06 inches) to about 2.0 millimeters (about 0.08inches).

Correspondingly, examples of suitable average cross-sectional areas forcore portion 36 range from about 0.5 square millimeters to about 5square millimeters. In one embodiment, suitable average cross-sectionalareas for core portion 36 range from about 0.75 square millimeters toabout 2 square millimeters.

Examples of suitable average cross-sectional areas for filament 34 rangefrom about 0.5 square millimeters to about 8 square millimeters. In oneembodiment, suitable average cross-sectional areas for filament 34 rangefrom about 1 square millimeter to about 3 square millimeters. In anotherembodiment, suitable average cross-sectional areas for filament 34 rangefrom about 1 square millimeter to about 2 square millimeters. In yetanother embodiment, suitable average cross-sectional areas for filament34 range from about 2 square millimeters to about 3 square millimeters.

The use of cross-sectional areas is also suitable for determining thecross-sectional dimensions of the composite filaments of the presetdisclosure that have non-cylindrical geometries (e.g., oval, oblong,round, rectangular, triangular, star-shaped, and the like), as discussedbelow. FIG. 3 illustrates a composite filament with a rectangulargeometry. The cross-sectional areas for composite filaments can vary anddepend on the intended use. For example, average cross-sectional areasfor a non-cylindrical consumable filament of the present disclosurerange from about 0.25 square millimeters to about 10 square millimeters.In some exemplary embodiments, the dimensions of the ribbon filament canbe between about 0.25 mm to about 1 mm in one cross-sectional dimension,and about 1 mm to about 10 mm in the other cross-sectional dimension.Dimensions outside of these ranges are also within the scope of thisdisclosure.

Suitable volumes and cross-sectional areas for shell portion 38 may bedetermined based on these above-discussed suitable cross-sectionalareas. Examples of suitable average volumes for shell portion 38 rangefrom about 5% to about 95% of the average volume of filament 34. In oneembodiment, suitable average volumes for shell portion 38 range fromabout 15% to about 65% of the average volume of filament 34. In anotherembodiment, suitable average volumes for shell portion 38 range fromabout 25% to about 60% of the average volume of filament 34.

Correspondingly, in embodiments in which core portion 36 and shellportion 38 are each substantially uniform along longitudinal length 40,examples of suitable average cross-sectional areas for shell portion 38range from about 5% to about 95% of the average cross-sectional area offilament 34. In one embodiment, suitable average cross-sectional areasfor shell portion 38 range from about 15% to about 65% of the averagecross-sectional area of filament 34. In another embodiment, suitableaverage cross-sectional areas for shell portion 38 range from about 25%to about 55% of the average cross-sectional area of filament 34.

Filament 34 may be manufactured with a co-extrusion process, where thecore and shell materials may be separately compounded and co-extruded toform filament 34. Other methods for manufacturing filament 34 may alsobe utilized and all are within the scope of this disclosure. FIG. 4shows an exemplary embodiment of a co-extrusion process formanufacturing a composite filament described herein. Co-extrusion line500 includes extruder 510 and extruder 520. An exemplary extruder 510 isa line screw extruder and is used for extruding core portion 36 thatincludes particles 50. An exemplary extruder 520 is a pressure-limitedextruder for extruding shell portion 38. Co-extrusion line 500 includescooling unit 530 to cool the extrudate. After formation, filament 34 maybe packaged for use with system 10 (e.g., within supply source 20).Filament 34, for example, can also be measured by laser micrometer 536and linked to pulley system 540 to attain spool 544 of consumablecomposite filament. Co-extrusion line 500 may include coaxial linecontrol panel 550 and floor drain 560.

In co-extrusion line 500, the rotational speed of the screw withinextruder 510 may be varied. Changes in the speed of the screw inextruder 510 can lead to volumetric differences of the core/shell in thefilaments. Increasing the speed of the extrusion screw can result indecreasing the volume of the shell portion in the filament. FIG. 5 showsthe variation in the cross-sections of filaments produced as the speedof the extrusion screw of the core shell extruder 570 is increased. FIG.5 shows that the percentage of volume of the core portion in thefilament increases as the speed of extrusion screw in extruder 510increases. In other words, the volume of the shell portion decreaseswith the increasing speed of the core portion extrusion. In theillustrated example of FIG. 5, the volume of the core portion can changefrom about 70 percent of the filament at 4 about rpm to about 86 percentof the filament at about 10 rpm.

FIG. 6 illustrates a build operation to build printed part 24 (shown inFIG. 1) from the filament 34 (shown in FIG. 2). As discussed above,during a build operation with system 10 (shown in FIG. 1), filament 34is fed to extrusion head 18 in a solid state from supply source 20.During feeding of filament 34 to extrusion head 18, the core portion mayhave breaks but filament 34 can still be utilized and is functional aslong as the shell portion is intact. While passing through extrusionhead 18, filament 34 is heated in a liquefier to a temperature that isgreater than the melting temperatures of the shell and core materials.The molten materials are then deposited onto build substrate 14 or otherprinted layers from extrusion nozzle 82 of extrusion head 18 in a seriesof extruded roads to form layers 84 of printed part 24. One or morelayers of a support material (not shown) may also be deposited belowlayers 84 to facilitate the removal of printed part 24 from buildsubstrate 14.

In the shown example, the extruded roads of the core materials and shellmaterials may at least partially, preferably substantially, retain theircore/shell profile from filament 34. For example, top extruded road 86includes core region 88 of the core material with particles 92 in thecore material and shell region 90 of the shell material, where shellregion 90 may extend around and encase core region 88. In oneembodiment, at least a portion of the extruded road partially retainsthe core/shell cross-sectional profile from filament 34. In a furtherembodiment, the extruded roads substantially retain their core/shellcross-sectional profile from filament 34.

While not wishing to be bound by theory, it is believed that asubstantially laminar flow of the molten core and shell materialsthrough a liquefier of extrusion head 18 may allow the extruded roads(e.g., road 86) to at least partially retain their core/shell profile.This laminar flow can be maintained, for example, when the viscosity ofthe core and shell materials is mismatched. It is understood thatinterdiffusion of the molten core and shell materials may occur at theinterface between core region 88 and shell region 90, particularly whenthe viscosities of the core and the shell materials are similar ormatched. As such, the resulting extruded roads (e.g., road 86) mayexhibit a cross-sectional profile that is the same or substantiallysimilar to that of filament 34 (as shown in FIG. 2), may exhibit a blendof the core and shell materials, or may exhibit a cross-sectionalprofile that is a variation between these two profiles (e.g., a profilein which the core and shell materials are partially interdiffused).

It is understood that the extruded roads (e.g., road 86) are typicallyflattened during the build operation due an ironing effect fromextrusion tip 82 caused by pressure between a distal end of theextrusion tip and the previously deposited layer. As such, having across-sectional profile that is the same or substantially similar tothat of the filament does not necessarily mean that the cross-sectionalshapes are the same (e.g., both are circular). Rather, this phrase meansthat the core material remains encased (or at least partially encased)in the shell material and the particles of the core material do notpenetrate the outer surface of the shell portion.

As discussed above, build chamber 12 is desirably heated to one or moresuitable temperatures to allow the extruded roads to solidify in one ormore stages. In one embodiment, the envelope of build chamber 12 mayoptionally be heated and maintained at one or more temperatures that areabout equal to, or within a small range above or below, thesolidification temperature of the shell and/or the core material. Uponbeing deposited into build chamber 12, the molten core and shellmaterials of road 86 cool from the elevated liquefier temperature withinextrusion head 18 to the temperature(s) of build chamber 12. Thisdesirably cools road 86 so that the shell and/or core material cansolidify. The shell material desirably solidifies in less time than isrequired to build a single layer of printed part 24, such that the shellmaterial exhibits at least about 30% solidification prior to thedeposition of a subsequent layer, and more desirably at least about 50%solidification. While a heated chamber is discussed, the presentcore/shell filament can be utilized in an additive manufacturing systemwithout a heated chamber or in an out of oven system. Some particles orfiller types may lend themselves to no chamber or active cooling due tothe increased heat capacity of the matrix.

In an alternative embodiment, the envelope of build chamber 12 may bemaintained at one or more temperatures that define a temperaturegradient that decreases in a downward direction along the verticalz-axis. For example, the upper region of build chamber 12 may be heatedand maintained at one or more temperatures that are about equal to, orwithin a small range above or below, the Tg temperature of the coreand/or shell material. The lower region of build chamber 12, however,may be maintained at one or more lower temperatures. For example, thelower region of build chamber 12 may be heated and maintained at one ormore temperatures that are about equal to, or within a small range aboveor below, the solidification temperature of the core and/or shellmaterial. As build substrate 14 lowers downward in an incremental manneralong the vertical z-axis, the gradual or stepwise cooling may allow thecore and/or shell material to slowly harden over time as subsequentlayers are built.

The composite filaments described herein can be used in a method ofprinting 3D parts. The composite filament can be provided, for example,in consumable assemblies in a variety of forms for use in an additivemanufacturing system. The filament can be provided, for example, tosystem 10 having print head 18 within consumable assembly 22. System 10may operate with preset instructions for extruding melt 70 at desiredflow rates based on tool path geometries. These preset instructions arepreferably based on the thermal properties of the consumable material,namely the melting rate and viscosity of the composite filament. Themethod includes printing the part in a layer by layer manner utilizingan additive manufacturing system. FIG. 7 shows a series of photographsof a cross-section of a printed part built using a composite filamentdescribed herein. The cross-section of the printed part can be seen tomaintain the core/shell cross-sectional profile of the compositefilament within the printed part.

If the printed parts require support structures, any suitable supportmaterials may be used in conjunction with the consumable assembliesdescribed herein. The support materials selected can be dependent on theproperties of the composite filaments.

Additionally, the core portions of the composite filaments may vary fromthe embodiments discussed above for filament 34. For example, in someembodiments, the core portions (e.g., core portion 36) may be locatedoff-axis from the central axis of the composite filament. In additionalalternative embodiments, the geometries of the core portions may benon-cylindrical (e.g., oval, oblong, round, rectangular, triangular, andthe like) and/or hollow to modify the characteristics of the resultingextruded roads. For example, as shown in FIG. 3, filament 234 is similarto filament 34 (shown in FIG. 2), where the respective reference labelsare increased by “200”. As shown in FIG. 3, filament 234 includes anon-cylindrical cross-sectional geometry with core portion 236 and shellportion 238 each having a rectangular cross-sectional geometry. Examplesof suitable materials for core portion 236 and shell portion 238 includethose discussed above for core portion 36 and shell portion 38 (shown inFIG. 2).

Suitable cross-sectional areas include those discussed above. Forexample, suitable average cross-sectional areas for core portion 236range from about 0.25 square millimeters to about 0.75 squaremillimeters. Correspondingly, examples of suitable averagecross-sectional areas for filament 234 range from about 0.5 squaremillimeters to about 1.5 square millimeters.

Filaments 34, and 234, shown above, illustrate suitable consumablematerials of the present disclosure that compositionally include same orsubstantially similar polymeric materials. In additional embodiments ofthe present disclosure, the consumable materials may compositionallyinclude core and shell materials with different polymeric materials thatimpart different properties. In these embodiments, the consumablematerials may be used as modeling materials to build printed parts(e.g., printed part 24), as support materials to build supportstructures (e.g., support structure 26), or both, where the differentmaterial properties may assist in the build operations withextrusion-based additive manufacturing systems, such as system 10.

The consumable materials of the present disclosure may include a varietyof different core and shell materials. This allows the modelingmaterials and/or the support materials to be designed for compatibilitywith each other and for use in extrusion-based additive manufacturingsystems, thereby increasing the range of suitable materials for buildingprinted parts and support structures.

EXAMPLES

The present disclosure is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present disclosurewill be apparent to those skilled in the art. Unless otherwise e and allreagents used in the examples were obtained, or are available, from thechemical suppliers described below, or may be synthesized byconventional techniques.

Example 1

Consumable filaments were coextruded in a core and shell arrangementcorresponding to filament 34 (shown in FIG. 2). The core material of thecore portion included ASA commercially available from A. Shulman,Fairlawn, Ohio. The particles were coated with an interfacial modifierchemistry to aid in incorporation into the polymer. The core materialalso includes ferrite particles purchased from Sigma Aldrich Corp., St.Louis, Mo. The ferrite particles purchased from Sigma Aldrich Corp., St.Louis, Mo. were added at about 55% by volume of the core material. Theshell material was also ASA and the same material as used for the corematerial. The shell material may be dyed with a white colorant tovisibly distinguish the core portion from the shell portion.

FIG. 5 includes photographs of cross-sectional segments of the compositefilaments. The shell portions of the composite filaments are shown withlighter shade due to the colorant dyes. The core portions of thefilaments with the ferrite particles are shown with darker shades. Thefilaments were coextruded with varying feed rates of the core portion tovary the volume fractions for the shell portions. The filament shown inFIG. 5 had an average core portion volume fraction that varied fromabout 70% at about 4 rpm to about 86% at about 8 rpm. The rpm of theextrusion of the core portion was varied.

Example 2

Cross section of filaments of Example 1 were then used to build printedparts. FIG. 7 is a photograph of printed parts built with the exemplaryfilaments. The printed part shown in FIG. 7 was a bar. Each printed partwas built in an extrusion-based additive manufacturing systemcommercially available from Stratasys, Inc., Eden Prairie, Minn. underthe trade designation “FDM TITAN”. The filaments were melted in anextrusion head liquefier of the system at a set temperature range of260° C. to 300° C., which was greater than the melting temperatures ofthe core and shell materials.

The molten materials were then extruded and deposited into a buildenvironment envelope maintained at a temperature range of about 160° C.to 180° C.

The printed part had a lighter shell color and a darker core portioncolor with the particles. This shows that the extruded roads of themolten materials retained a core/shell cross-sectional profile.Furthermore, printed parts built with different volumes of shell portionmaintain the cross-sectional profile of the filament. As the shelldecreased in volume, (extrusion speed of core portion during filamentformation from 4 rpm to 7 rpm), the cross-sectional profile of thefilament is maintained indicative that laminar flow was notsubstantially disrupted.

Although the present disclosure has been described with reference toseveral embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the disclosure.

1-19. (canceled)
 20. A method of printing a 3D part utilizing anextrusion-based additive manufacturing system, the method comprising:providing a consumable filament to a print head of the extrusion basedadditive manufacturing system, the filament comprising: a core portionextending along a longitudinal length of the consumable filament, thecore portion compositionally comprising a matrix of a first base polymerand particles dispersed in the matrix; and a shell portion extendingalong the longitudinal length of the consumable filament and at leastpartially encasing the core portion, the shell portion compositionallycomprising a second base polymer, heating the filament in a liquefier ofthe print head such that the first and second base polymers are in amolten state; and extruding the material from a print head nozzle influid communication with the liquefier in a layer-by layer manner toprint the 3D part wherein each layer comprises a series of roads andwherein the extruded material retains a core-shell configuration. 21.The method of claim 20, wherein the first base polymer and the secondbase polymer are the same.
 22. The method of claim 20, wherein the firstbase polymer and the second base polymer are different.
 23. The methodof claim 20, wherein a glass transition temperature of the first basepolymer and the second base polymer are substantially similar.
 24. Themethod of claim 20, wherein a rheology of the first base polymer and thesecond base polymer are substantially similar.
 25. The method of claim20, wherein a viscosity of the core portion is different than theviscosity of the shell portion and wherein the filament displays laminarflow when melted such that the core-shell configuration is retained. 26.The method of claim 20, wherein the particles are selected from metallicparticles, non-metallic particles, magnetic particles and combinationsthereof.
 27. The method of claim 20, wherein the particles are ferriteparticles, stainless steel particles or combinations thereof.
 28. Themethod of claim 20, wherein the particles comprise between at leastabout 50 percent by volume and about 85 percent by volume of the coreportion.
 29. The method of claim 20, wherein the particles comprisebetween at least about 55 percent by volume and about 85 percent byvolume of the core portion.
 30. The method of claim 20, wherein thefilament has a geometry selected from a cylinder, a ribbon, and otherfilled profiles.
 31. The method of claim 20, wherein the shell portioncomprises Acrylonitrile Styrene Acrylate (ASA) and the core portioncomprises ASA-ferrite.
 32. A method of printing a 3D part utilizing anextrusion-based additive manufacturing system, the method comprising:providing a consumable filament to a print head of the extrusion basedadditive manufacturing system, the filament comprising: a core portionextending along a longitudinal length of the consumable filament, thecore portion compositionally comprising a matrix of a first base polymerand metallic particles dispersed in the matrix; and a shell portionextending along the longitudinal length of the consumable filament andat least partially encasing the core portion, the shell portioncompositionally comprising a second base polymer, heating the filamentin a liquefier tube such that the first and second base polymers are ina molten state; extruding the material from a print head nozzle in fluidcommunication with the liquefier tube in a series of roads to form afirst layer of the 3D part; and extruding the material from the printhead nozzle onto the first layer in a series of roads to form a secondlayer of the 3D part wherein the extruded material displays laminar flowwhen melted and extruded such that a core-shell configuration isretained through the extrusion process.
 33. The method of claim 32,wherein the first base polymer and the second base polymer are the same.34. The method of claim 32, wherein the first base polymer and thesecond base polymer are different.
 35. The method of claim 32, wherein aglass transition temperature of the first base polymer and the secondbase polymer are substantially similar.
 36. The method of claim 32,wherein a rheology of the first base polymer and the second base polymerare substantially similar.
 37. The method of claim 32, wherein themetallic particles comprise ferrite particles, stainless steel particlesor combinations thereof.
 38. The method of claim 20, wherein themetallic particles comprise between at least about 50 percent by volumeand about 85 percent by volume of the core portion.
 39. The method ofclaim 20, wherein the metallic particles comprise between at least about55 percent by volume and about 85 percent by volume of the core portion.